Heretofore yeast cells such as Torula yeast and beer yeast have been utilized as feed for livestock.
However, some livestock cannot be sufficiently supplied with some amino acids from yeast cell source alone. For example, domestic fowls tend to suffer from insufficiency of L-arginine. Insufficient amino acids are supplemented by addition of each amino acid, but this is not economically advantageous. If various kinds of yeasts are provided which are capable of accumulating insufficient amino acids in the cells in large quantities, the yeast cells would be widely utilized as feed for livestock.
As yeast capable of accumulating L-arginine in the cells in large quantities, there is known a regulatory mutant (argR, cpoO) belonging to the genus Saccharomyces which accumulates 1.7% of L-arginine in the cells [Eur. J. Biochem., 12, No. 1, 40-47 (1970)].